Added fPowNoRetargeting field to Consensus::Params that disables nBits recalculation.

src/chainparams.cpp

@@ -76,6 +76,7 @@ public:
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = false;
+        consensus.fPowNoRetargeting = false;
         /** 
          * The message start string is designed to be unlikely to occur in normal data.
          * The characters are rarely used upper ASCII, not valid as UTF-8, and produce
@@ -155,6 +156,7 @@ public:
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
+        consensus.fPowNoRetargeting = false;
         pchMessageStart[0] = 0x0b;
         pchMessageStart[1] = 0x11;
         pchMessageStart[2] = 0x09;
@@ -217,6 +219,7 @@ public:
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
+        consensus.fPowNoRetargeting = true;
 
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0xbf;

src/consensus/params.h

@@ -22,6 +22,7 @@ struct Params {
     /** Proof of work parameters */
     uint256 powLimit;
     bool fPowAllowMinDifficultyBlocks;
+    bool fPowNoRetargeting;
     int64_t nPowTargetSpacing;
     int64_t nPowTargetTimespan;
     int64_t DifficultyAdjustmentInterval() const { return nPowTargetTimespan / nPowTargetSpacing; }

src/pow.cpp

@@ -52,6 +52,9 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
 
 unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nFirstBlockTime, const Consensus::Params& params)
 {
+    if (params.fPowNoRetargeting)
+        return pindexLast->nBits;
+
     // Limit adjustment step
     int64_t nActualTimespan = pindexLast->GetBlockTime() - nFirstBlockTime;
     LogPrintf("  nActualTimespan = %d  before bounds\n", nActualTimespan);